practice round: dead session starts, prompt laws, preamble, label unify

THE START BUG (owner report, reproduced live both kinds): new sessions
(?prompt flow — practice and teach alike) sat dead until a second
message, which then persisted WITHOUT the first. Root cause, proven
both directions: the submit POST rode the view's consumeAbort
controller; React StrictMode's simulated remount fires Diet A's
unmount cleanup (model.stop()) ~8ms in and killed the POST mid-flight;
the page's sentInitial guard had already flipped, so it never retried.
Teach was equally broken — only unnoticed, because every teach chat in
use predates the diet and practice starts are always fresh. Fix: the
submit law — POSTs are not abortable by view teardown (they are ~100ms
acks since Diet B and cannot starve the pool); after the ack, a
consumeAbort identity check guards the stream attach. Pinned with the
stop-mid-submit regression test. Live: StrictMode on, practice draft
POST 200/67ms, stream attached, message persisted, problem posed.

PRACTICE PROMPT (00-base): the opening rule — material arrives two
ways, both first-class (picked propositions primary; free-form —
topics, course material, files/PDFs — fully supported, never refused);
as soon as material exists the reply poses, at most one short line
before the problem call, no warm-up interview. Plus the hard law: no
problem is ever conversation — every problem through the tool (no
thinking field/no reveal/no verdict attaches to prose).

GRAPH-CONTEXT PREAMBLE: custom markers flatten to user-role on the
wire, so the old "Contextualization — the learner picked…" read like a
system broadcast in the learner's voice channel. Now the bracket
convention: "[Session context] — picked from the learner's knowledge
map…".

SIDEBAR: busy rows unify to "Working…" for both kinds (the spinner's
default label included); "Practicing…"/"Teacher is working…" retired.

Gates: 1490/1490, typecheck, lint. doctrine's stale doc pointer fixed.

src/core/native-messages.ts

@@ -213,7 +213,12 @@ export function newGraphContextMessage(picks: readonly GraphContextPick[], chain
 	// ids at the seam). Chains below stay NAMES — they are comprehension
 	// context, not tags; names read, ids reference.
 	const lines = [
-		"Contextualization — the learner picked these propositions from their knowledge map when starting this session:",
+		// PREAMBLE LAW (owner, 2026-10-10): custom markers flatten to
+		// USER-role messages on the wire (toLlmMessages) — this text arrives
+		// in the learner's voice channel, so it must not read like a system
+		// broadcast. The bracket convention (NEXT_PROBLEM_TEXT's kin) marks
+		// it honestly as injected session context, not learner speech.
+		"[Session context] — picked from the learner's knowledge map when starting this session:",
 		"",
 		"Propositions (id — name: statement; the problem tool's target field uses these ids):",
 		...picks.map((p) => `- [${p.id}] ${p.name}: ${p.statement}`),